The invention relates to apparatus for controlling valves that move linearly along respective axes, the apparatus comprising as many actuators as there are valves, each actuator having an armature of ferromagnetic material fixed to a valve push rod that is movable in a housing of the actuator by electromagnetic means having at least one coil mounted on a ferromagnetic circuit and having at least one return spring with one end bearing against the rod.
Apparatuses of this kind can have two opposing return springs (U.S. Pat. No. 4,614,170 or French patent application No. 98/12489) or a single spring working alternately in traction and in compression (French patent No. 2,783,631). The electromagnetic means of an actuator can have two coils which, when excited, tend to move the armature in opposite directions. It is also possiblexe2x80x94and this solution is generally preferable for reasons of cost, compactness, and reducing the number of electrical connectionsxe2x80x94for them to use a single coil whose ferromagnetic circuit is of a structure such as to cooperate with the armature to provide two stable magnetic flux paths corresponding to a valve-open state and to a valve-closed state, repetitively (French patent No. 2,784,222 and corresponding European application).
Such apparatus has as many actuators as there are valves. On an engine having sixteen valves arranged in two rows, eight actuators need to be placed side by side. The power of an actuator is limited, forgiven thickness, and this thickness is itself limited because the actuators must be distributed in the same way as the valves. On engines of low cylinder capacity, the power which can be obtained with individual actuators can be insufficient, at least for exhaust valves since they are the most demanding under high engine loads because of the back pressure in the combustion chamber. Furthermore, the need for one electrical power connector per actuator is expensive and reduces reliability.
An object of the invention is to provide valve control apparatus for an engine having two valves of the same type per cylinder, having increased compactness and reliability
To this end, the invention provides apparatus in which the ferromagnetic circuits of the two actuators allocated to two valves of the same type for a single cylinder are contained in a common housing, and the coils of the two actuators can consequently be powered by a single power connector. The single connector can additionally be used for conveying measurement signals to the outside from a sensor for sensing the position of the armature.
In another aspect, the invention provides apparatus in which the ferromagnetic circuits of two actuators allocated to two valves of the same type for a single cylinder are merged. Not only does this disposition reduce overall size and thus make it possible locally to increase the iron section by taking advantage of the empty space between two cylinders, but it also makes it possible to increase the section of the common portion which is entirely beneficial for driving a single one of the valves while the other one remains at rest, e.g. when starting valve oscillation.
The invention is particularly easy to implement with single-coil actuators where it is also possible for sensors for sensing the axial position of the rod and of the armature, by detecting the position of a permanent magnet fixed to the rod, to be placed in a zone where the magnetic flux created by the coil is always very small and does not disturb operation because of the symmetry of the planar graph of the stream lines.
The above characteristics and others will appear more clearly the following description of a non limiting embodiment. The description refers to the accompanying drawings.